TREACHERY

 Treachery-gadr- is not to keep one’s word and agreement.

 Giving a word of someone to another is a promise. The mutual agreement of both sides is a contract. A promise which is strengthened by an oath is a compact-misaq. In a mutual agreement going back one’s word without informing the other side is treachery -gadr because this will be harmful to the other.
When a Muslim ruler realizes that he should cancel the agreement that is done by infidels, it’s a due to inform them. It’s not proper to cancel before warning. In a hadith it is said that: “A treacherous person will be punished severely in doomsday”. To commit treachery is prohibited. To keep the promise even if it’s made to infidels is a due.

 Again our Prophet (peace be upon him) declared: “Who is not trustworthy, has no faith. Who goes back his word has no religion.”